Download chapter42_Sections 7

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 42
Ecosystems
(Sections 42.7 - 42.10)
Albia Dugger • Miami Dade College
42.7 The Water Cycle
• 97% of Earth’s water is in its oceans
• Sunlight energy drives the water cycle by causing
evaporation – water vapor in the atmosphere condenses into
clouds, and returns to Earth’s surface as precipitation
• water cycle
• Movement of water among Earth’s oceans, atmosphere,
and the freshwater reservoirs on land
Environmental Water Reservoirs
Reservoir
•
•
•
•
•
Volume (103 cubic kilometers)
Ocean
Polar ice, glaciers
Groundwater
Lakes, rivers
Atmosphere (water vapor)
1,370,000
29,000
4,000
230
14
The Water Cycle
The Water Cycle
Atmosphere
Evaporation
from ocean
Precipitation
into ocean
Windborne water vapor
Evaporation
from land plants
(transporation)
Precipitation
onto the land
Surface and
groundwater
flow
Land
Ocean
Fig. 42.8, p. 715
The Water Cycle
Atmosphere
Evaporation
from ocean
Precipitation
into ocean
Windborne water vapor
Evaporation
from land plants
(transporation)
Precipitation
onto the land
Surface and
groundwater
flow
Land
Ocean
Stepped Art
Fig. 42.8, p. 715
How and Where Water Moves
• Precipitation that falls on any specific area of land drains into
its particular watershed
• A watershed may be as small as a valley that feeds a stream,
or as large as the Mississippi River Basin (drains 41% of the
continental United States)
• watershed
• Land area that drains into a particular stream or river
How Water Moves (cont.)
• Most precipitation seeps into the ground (groundwater):
• Clay-rich soils hold the most soil water and sandy soils
hold the least
• Water that drains through soil layers often collects in
natural underground reservoirs (aquifers)
• The flow of groundwater and surface water (runoff) slowly
returns water to oceans
Key Terms
• groundwater
• Soil water and water in aquifers
• soil water
• Water between soil particles
• aquifer
• Porous rock layer that holds some groundwater
• runoff
• Water that flows over soil into streams
Nutrients in Water
• Important nutrients such as carbon, nitrogen, and phosphorus
have soluble forms that can be moved from place to place by
flowing water
• Runoff from heavily fertilized lawns and agricultural fields
carries dissolved phosphates and nitrates into streams and
lakes, causing eutrophication
Limited Fresh Water
• Groundwater (a limited resource) supplies drinking water to
about half of the United States population
• Water is being drawn from aquifers faster than natural
processes can replenish it (groundwater overdrafts)
• In coastal aquifers, salt water moves in and replaces fresh
water (saltwater intrusion)
• In the US, about 80% of the water withdrawn for human use
ends up irrigating agricultural fields
Groundwater Troubles
Key Concepts
• The Water Cycle
• Most of Earth’s water is in its oceans
• Only a tiny fraction is fresh water
• Evaporation, condensation, precipitation, and flow of rivers
and streams moves water
• Water plays a role in other nutrient cycles because it
carries soluble forms of those nutrients with it
Animation: Threats to Aquifers
42.8 The Carbon Cycle
• The carbon cycle is an atmospheric cycle
• Most carbon is stored in rocks – it enters food webs as
gaseous carbon dioxide or bicarbonate dissolved in water
• carbon cycle
• Movement of carbon, mainly between the oceans,
atmosphere, and living organisms
• atmospheric cycle
• Biogeochemical cycle in which a gaseous form of an
element plays a significant role
6 Steps in the Carbon Cycle
• Carbon in rocks is largely unavailable to living organisms
1. Carbon enters land food webs when plants use CO2 from the
air in photosynthesis
2. CO2 released by aerobic respiration returns to the
atmosphere
3. Carbon diffuses between atmosphere and ocean;
bicarbonate forms when CO2 dissolves in seawater
6 Steps in the Carbon Cycle
4. Marine producers take up bicarbonate for photosynthesis;
marine organisms release CO2 from aerobic respiration
5. Many marine organisms incorporate carbon into shells
• Shells become part of sediments
• Sediments become limestone and chalk in Earth’s crust
6. Burning fossil fuels derived from ancient remains of plants
puts additional CO2 into the atmosphere
6 Steps in the Carbon Cycle
6 Steps in the Carbon Cycle
Atmospheric CO2
1 photosynthesis
6 burning fossil fuels
2
aerobic respiration
diffusion between
3atmosphere and
ocean
Land food webs
Dissolved carbon
in ocean
4
Fossil fuels
death, burial,
compaction over
millions of years Earth’s crust
Marine
organisms
sedimentation
5
1 Carbon enters land food webs when
plants take up carbon dioxide from the
air for use in photosynthesis.
2 Carbon returns to the atmosphere as
carbon dioxide when plants and other land
organisms carry out aerobic respiration.
3 Carbon diffuses between the atmosphere
and the ocean. Bicarbonate forms when
carbon dioxide dissolves in seawater.
4 Marine producers take up bicarbonate for use in
photosynthesis, and marine organisms release carbon
dioxide from aerobic respiration.
5 Many marine organisms incorporate carbon into their
shells. After they die, these shells become part of the
sediments. Over time, the sediments become carbon-rich
rocks such as limestone and chalk in Earth’s crust.
6 Burning of fossil fuels derived from the ancient
remains of plants puts additional carbon dioxide into
the atmosphere.
Fig. 42.10, p. 716
6 Steps in the Carbon Cycle
Atmospheric CO2
6 burning fossil fuels
1 photosynthesis
2
aerobic respiration
diffusion between
3atmosphere and
ocean
Land food webs
4
Fossil fuels
death, burial,
compaction over
millions of years Earth’s crust
Dissolved carbon
in ocean
Marine
organisms
sedimentation
5
Stepped Art
Fig. 42.10, p. 716
Animation: Carbon Cycle
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Carbon, the Greenhouse Effect,
and Global Warming
• Atmospheric CO2 and other “greenhouse gases” help keep
Earth warm enough for life through the greenhouse effect
• greenhouse effect
• Warming of Earth’s lower atmosphere and surface as a
result of heat trapped by greenhouse gases
Three Steps in the Greenhouse Effect
1. Earth’s atmosphere reflects some sunlight energy back into
space
2. Some light energy reaches and warms Earth’s surface
3. Earth’s warmed surface emits heat energy
• Some escapes into space
• Some is absorbed and emitted in all directions by
greenhouse gases
Three Steps in the Greenhouse Effect
Three Steps in the Greenhouse Effect
light
energy
3
1
heat
energy
2
Fig. 42.11, p. 717
Animation: Greenhouse Effect
Global Warming
• Human-induced increase in atmospheric greenhouse gases
correlates with global climate change
• Current atmospheric CO2 is the highest in 420,000 years –
and climbing
• global climate change
• A rise in temperature and shifts in other climate patterns
Key Concepts
• The Carbon Cycle
• Most of Earth’s carbon is tied up in rocks, but organisms
take carbon up from water or the air
• Carbon dioxide is one of the atmospheric greenhouse
gases that help keep Earth’s surface warm
• Increasing carbon dioxide in the air is the most likely
cause of climate change
BBC Video: Carbon Dioxide’s Impact on Our
Oceans
42.9 The Nitrogen Cycle
• Nitrogen moves in an atmospheric cycle (nitrogen cycle)
• Atmospheric nitrogen (N2 or gaseous nitrogen) is Earth’s main
nitrogen reservoir, but most organisms can’t use N2
• nitrogen cycle
• Movement of nitrogen among the atmosphere, soil, and
water, and into and out of food webs
Bacteria and Nitrogen Conversions
• Only certain bacteria can make nitrogen available to other
organisms, or return N2 to the atmosphere
• nitrogen fixation
• Bacteria use nitrogen gas (N2) to form ammonia (NH3)
• nitrification
• Bacteria convert ammonium (NH4+) to nitrates (NO3-)
• denitrification
• Bacteria convert nitrates or nitrites (NO2-) to nitrogen gas
6 Steps in the Nitrogen Cycle
1. Nitrogen fixing cyanobacteria in soil, water, or lichens break
bonds in N2 and form ammonia, which is ionized in water as
ammonium (NH4+) and taken up by plants
2. Another group of nitrogen-fixing bacteria forms nodules on
roots of peas and other legumes
3. Consumers get nitrogen by eating plants or one another;
bacterial and fungal decomposers break down wastes and
remains and return ammonium to the soil
6 Steps in the Nitrogen Cycle
4. Nitrification converts ammonium to nitrates:
• Ammonia-oxidizing bacteria and archaeans convert
ammonium to nitrite (NO2–),
• Bacteria convert nitrites to nitrates (NO3–)
5. Nitrates are taken up and used by producers
6. Denitrifying bacteria use nitrate for energy and release
nitrogen gas into the atmosphere
The Nitrogen Cycle
The Nitrogen Cycle
Land food webs
1 nitrogen fixation
6 denitrification
Waste and
remains
by bacteria
2 uptake
by producers
Soil ammonium
(NH4+)
3 decomposition by
bacteria and fungi
4 nitrification
by bacteria
by bacteria
5 uptake
by producers
Soil nitrates
(NO3–)
Fig. 42.12, p. 718
The Nitrogen Cycle
Land food webs
1 nitrogen fixation
6 denitrification
Waste and
remains
by bacteria
2 uptake
by producers
Soil ammonium
(NH4+)
3 decomposition by
bacteria and fungi
4 nitrification
by bacteria
by bacteria
5 uptake
by producers
Soil nitrates
(NO3–)
Stepped Art
Fig. 42.12, p. 718
Animation: Nitrogen Cycle
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Human Effects on the Nitrogen Cycle
• Manufactured ammonia fertilizers increase the concentration
of hydrogen ions (H+) as well as nitrogen
• Nutrient ions bound to soil particles get replaced by H+,
and essential nutrients leach away in soil water
• Nitrogen runoff also pollutes aquatic habitats
• Burning fossil fuels releases nitrous oxide, a greenhouse gas
that also contributes to acid rain
• Nitrogen in acid rain has the same effects as fertilizers
42.10 The Phosphorus Cycle
• Most phosphorus is bonded to oxygen as phosphate (PO43– )
in rocks and sediments – and moves in a sedimentary cycle
• phosphorus cycle
• Movement of phosphorus among Earth’s rocks and
waters, and into and out of food webs
• sedimentary cycle
• Biochemical cycle in which the atmosphere plays little role
and rocks are the major reservoir
8 Steps in the Phosphorus Cycle
1. Weathering and erosion move phosphates from rocks into
soil, lakes, and rivers
2. Leaching and runoff carry dissolved phosphates to the ocean
3. Phosphorus comes out of solution and settles as deposits
along continental margins
4. Slow movements of Earth’s crust uplift deposits onto land,
where weathering releases phosphates from rocks
8 Steps in the Phosphorus Cycle
5. Land plants take up dissolved phosphate from soil water
6. Land animals get phosphates by eating plants or one
another; phosphorus returns to soil in wastes and remains
7. In seas, producers take up phosphate dissolved in seawater
8. Wastes and remains replenish phosphates in seawater
The Phosphorus Cycle
The Phosphorus Cycle
Land food webs
Rocks
on land
1
weathering,
5 uptake
erosion
by producers
excretion, death,
decomposition
6
2 leaching,
runoff
Phosphates in soil, lakes, rivers
7
Phosphates
in seawater
Marine
food web
8
3
4 uplifting over geologic time
Marine sediments
Fig. 42.13, p. 719
The Phosphorus Cycle
Land food webs
Rocks
on land
1
weathering,
excretion, death,
5
uptake
erosion
decomposition
by producers
6
2 leaching,
runoff
Phosphates in soil, lakes, rivers
7
Phosphates
in seawater
Marine
food web
8
3
4 uplifting over geologic time
Marine sediments
Stepped Art
Fig. 42.13, p. 719
Phosphates and Eutrophication
• Phosphorus is often a limiting factor for plant growth
• Phosphate-rich droppings from seabird or bat colonies are
used as fertilizer
• Phosphate-rich rock is also mined for this purpose
• Water pollution from high-phosphate fertilizers, detergents, or
sewage can cause eutrophication
Key Concepts
• Nitrogen and Phosphorus Cycles
• Plants take up dissolved forms of nitrogen and
phosphorus from soil water
• Nitrogen is abundant in air, but only certain bacteria can
use the gaseous form
• Phosphorus has no major gaseous form; most of it is in
rocks
Too Much of a Good Thing (revisited)
• Water treatment systems can remove phosphates from
household wastewater with additional treatment and cost
• Phosphate-rich runoff from lawns usually goes into waterways
without going through a treatment plant
• The most effective and economical way to keep aquatic
ecosystems healthy is to avoid using phosphate-rich products
when substitutes are available
Animation: Phosphorus Cycle